Policy-driven variations in oxidation potential and source apportionment of PM in Wuhan, central China.

China has implemented several control measures to mitigate PM pollution and improve air quality, such as the Action Plan for the Prevention and Control of Air Pollution (APPCAP). To comprehensively assess the changes in ambient PM concentrations and the corresponding health risk with the implementation of APPCAP, this study examined PM samples collected in Wuhan in 2012/2013 and 2018 for water-soluble ions, carbonaceous fractions, and elements, respectively. Dithiothreitol (DTT) assay was used to determine the oxidation potential (OP) of PM. The positive matrix factorization (PMF) model and the multiple linear regression (MLR) model were used to analyze PM sources and the contribution of each source to the OP of PM. The results showed that PM concentrations in Wuhan decreased significantly, however, there was little change in the health risk and a significant increase in intrinsic toxicity. DTT (the volume-normalized dithiothreitol) showed high correlations (r > 0.5, p < 0.01) with water-soluble organic carbon (WSOC), organic carbon (OC), secondary ions (NO, SO, and NH), and elements. Compared to 2012/2013, the contribution of vehicle emissions and secondary aerosol sources to PM increased significantly in 2018. Biomass burning sources significantly contribute to DTT in the summer and autumn, and secondary aerosol sources significantly contribute to DTT in winter. The human health impacts from coal combustion sources remained high, while vehicle emission sources increased. In the context of decreasing PM concentrations, the role of vehicle emissions health impacts is increasingly significant due to the large increment in vehicle ownership and high inherent OP. Therefore, targeting vehicle emissions for control is of great importance for human health and needs to be given great attention in future policymaking.